The present invention relates to a pneumatic tire including a reinforcing rope made of at least two components, whereby one component consists of steel wires and the second component of fibres of p-aromatic polyamides.
A reinforcing rope of this kind is described in U.S. Pat. No. 4,176,705. The prior art reinforcing rope is composed of a plurality of twisted strands of round steel wires coiled around a multi-filament core of aromatic polyamide. In order to keep the steel wire strands in mutually spaced relationship, breaking strength of respective strands is set equal to that of the core. However, if such a prior art rope is exposed to a tensile load, the core filaments of aromatic polyamide share the load with the steel wires whereby the polyamide core filaments are exposed to extremely strong transverse forces exerted by the steel strands. The effect of the transverse forces is very disadvantageous because the larger is the tensile load the larger is the extension and hence the stronger is the effect of transverse forces.
As known, steel wires have a lower breaking extension than have the filaments of aromatic polyamide. Consequently, the prior art composite reinforcing rope can be exposed to such a load only at which its extension does not exceed the breaking extension of the steel wire strands. If this limit load is exceeded, the steel wires rupture and the entire load is taken up by the polyamide core which in turn immediately exceeds its own breaking elongation and ruptures too. In other words, the known composite rope breaks when its extension corresponds to the breaking extension of its steel wire component in spite of the fact that the latter is distinctly below the breaking elongation of the polyamide core.
Since the breaking elongation of the prior art reinforcing rope is smaller than the sum of breaking elongations of its component parts, the excellent strength of the core filaments of aromatic polyamide is utilized only partially.